1. Field of the Invention
The present invention relates to an image-stabilizing zoom lens, and, more particularly, to an image-stabilizing zoom lens which is suited for a television camera, a photographic camera, a video camera or the like, and which has high optical performance over the entire range of variable magnification even during an image stabilizing operation, with the refractive power arrangement of the whole zoom lens, the arrangement of the moving lens units for the variation of magnification, and the construction of the fourth lens unit appropriately set.
2. Description of Related Art
Heretofore, for use with a television camera, a photographic camera, a video camera or the like, there has been a demand for a zoom lens having high optical performance while having a large relative aperture and a high variable magnification ratio. In addition to such a demand, in the case of a color television camera for broadcasting, in particular, importance is attached to operability and mobility. In response to such a requirement, the usage of a CCD (charge-coupled device) of ⅔ inch or xc2xd inch has become the mainstream for an image pickup device in the color television camera. Since the CCD has an almost uniform resolution over the entire image pickup range, a zoom lens to be associated with the CCD is also required to have an almost uniform resolution from the center of an image plane to the periphery thereof. For example, the zoom lens is required to have the various aberrations, such as coma, astigmatism and distortion, corrected well and to have high optical performance over the entire image plane. In addition, the zoom lens is required to have a large relative aperture, a wide angle of view and a high variable magnification ratio while being small in size and light in weight, and moreover to have a long back focal distance for enabling a color separation optical system and a variety of filters to be disposed in front of an image pickup means.
In addition, it has become a large problem to suppress an image shake caused by the vibration of a photographing system which has a long focal length or by the vibration of hands holding the photographing system. Accordingly, a demand for an image stabilizing function of preventing an image shake has risen. Under the circumstances, there have been proposed a variety of types of image stabilizing methods.
For example, in Japanese Laid-Open Patent Application No. Sho 61-223819 (corresponding to U.S. Pat. No. 4,927,250), there has been proposed a photographing system in which a refraction-type variable angle prism is disposed on the most object side (the side nearest to the object) of the photographing system so as to stabilize an image by varying an apex angle of the refraction-type variable angle prism according to the vibration of the photographing system.
Further, in Japanese Laid-Open Patent Application No. Hei 1-116619 (corresponding to U.S. Pat. No. 5,270,857 and Japanese Laid-Open Patent Application No. Hei 2-124521 (corresponding to U.S. Pat. No. 5,039,211), there has been proposed a method of obtaining a stationary image by detecting the vibration of a photographing system by means of an acceleration sensor or the like and causing a lens unit that is a part of the photographing system to shift in a direction perpendicular to the optical axis according to a signal obtained by the acceleration sensor or the like.
Further, in Japanese Laid-Open Patent Application No. Hei 8-29738 (corresponding to U.S. Pat. No. 5,721,641), there has been proposed a zoom lens comprising four lens units, i.e., in order from the object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of negative refractive power and a fourth lens unit of positive refractive power, in which the fourth lens unit is composed of a front lens subunit of positive refractive power and a rear lens subunit of positive refractive power, and the shaking of a photographed image caused by the vibration of the zoom lens is corrected by moving the front lens subunit in a direction perpendicular to the optical axis.
Further, in Japanese Laid-Open Patent Application No. Hei 10-90601 (corresponding to U.S. Pat. No. 6,025,962), there has been proposed a zoom lens comprising five lens units, i.e., in order from the object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power, a fourth lens unit of negative refractive power and a fifth lens unit of positive refractive power, in which the shaking of a photographed image caused by the vibration of the zoom lens is corrected by moving the fourth lens unit in a direction perpendicular to the optical axis.
Further, in Japanese Laid-Open Patent Application No. Hei 7-27978 (corresponding to U.S. Pat. No. 5,760,957), there has been proposed a zoom lens comprising four lens units, i.e., in order from the object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of negative refractive power and a fourth lens unit of positive refractive power, in which the fourth lens unit is composed of a front lens subunit of positive refractive power and a rear lens subunit of positive refractive power, and the shaking of a photographed image caused by the vibration of the zoom lens is corrected by moving the third lens unit or the front lens subunit in a direction perpendicular to the optical axis.
In general, the method of obtaining a stationary image by disposing an image-stabilizing optical system in front of a photographing system and driving and controlling a movable lens unit that is a part of the image-stabilizing optical system to prevent the shaking of a photographed image would cause the whole apparatus to become large in size and a moving mechanism for moving the movable lens unit to become complicated.
In an optical system in which the image stabilization is performed by means of a variable angle prism, the amount of occurrence of decentering lateral chromatic aberration would become large, in particular, on the telephoto side during the image stabilization.
On the other hand, in an optical system in which the image stabilization is performed by causing a lens unit that is a part of a photographing system to decenter in a direction perpendicular to the optical axis, although there is such an advantage that it is unnecessary to provide a specific optical system used for the image stabilization, a space would be required for the lens unit to be moved and the amount of occurrence of decentering aberration during the image stabilization would become large.
In particular, in the four-unit zoom lens composed of four lens units of positive, negative, negative and positive refractive powers, respectively, in which the image stabilization is performed by moving the front lens subunit of positive refractive power of the fourth lens unit in a direction perpendicular to the optical axis, as proposed in the above-mentioned Japanese Laid-Open Patent Application No. Hei 8-29738, the front lens subunit, serving as an image-stabilizing lens unit, is a positive lens unit having a relatively small image-stabilizing effect (the amount of movement of the optical axis relative to the amount of decentering being small), and, as a result, there is a possibility that the amount of movement of the image-stabilizing lens unit becomes large to cause an increase of the size of a driving mechanism for the image-stabilizing lens unit.
Further, in particular, in the five-unit zoom lens composed of five lens units of positive, negative, positive, negative and positive refractive powers, respectively, in which the image stabilization is performed by moving the fourth lens unit in a direction perpendicular to the optical axis, as proposed in the above-mentioned Japanese Laid-Open Patent Application No. Hei 10-90601, since the fourth lens unit is a lens unit arranged to move in the optical axis direction during the variation of magnification, a driving control mechanism for the fourth lens unit would become complicated.
It is an object of the invention to provide a zoom lens having high optical performance over the entire range of variable magnification even during an image stabilizing operation, with the whole mechanism of the zoom lens reduced in size and weight, and a photographing apparatus using the zoom lens.
To attain the above object, in accordance with a first aspect of the invention, there is provided a zoom lens comprising, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power arranged to move during variation of magnification, a third lens unit of negative refractive power arranged to compensate for shift of an image plane due to the variation of magnification, and a fourth lens unit of positive refractive power, wherein the fourth lens unit has a focal-length changeover subunit arranged to be insertable onto and detachable from an optical axis of the zoom lens and provided for changing the focal length of the zoom lens, and an image-stabilizing lens subunit disposed on the object side of the focal-length changeover subunit, and the image-stabilizing lens subunit is movable in such a way as to have a component perpendicular to the optical axis so as to displace an image.
In accordance with a preferred aspect of the invention, in the zoom lens, the image-stabilizing lens subunit has a positive refractive power.
In accordance with a preferred aspect of the invention, in the zoom lens, the image-stabilizing lens subunit has at least one positive lens and at least one negative lens.
In accordance with a preferred aspect of the invention, in the zoom lens, the image-stabilizing lens subunit is disposed within a diverging light flux exiting from the third lens unit, and the following condition is satisfied:
0.45 less than (xcex1xe2x80x2xe2x88x92xcex1)
where xcex1 is a converted inclination angle of incidence of a ray entering the fourth lens unit, and xcex1xe2x80x2 is a converted inclination angle of exit of a ray exiting from the image-stabilizing lens subunit.
In accordance with a preferred aspect of the invention, in the zoom lens, the following condition is satisfied:
30 less than (xcexdpxe2x88x92xcexdn)
where xcexdp is, when the image-stabilizing lens subunit includes only one positive lens, an Abbe number of the positive lens included in the image-stabilizing lens subunit or, when the image-stabilizing lens subunit includes a plurality of positive lenses, a mean value of Abbe numbers of all the positive lenses included in the image-stabilizing lens subunit, and xcexdn is, when the image-stabilizing lens subunit includes only one negative lens, an Abbe number of the negative lens included in the image-stabilizing lens subunit or, when the image-stabilizing lens subunit includes a plurality of negative lenses, a mean value of Abbe numbers of all the negative lenses included in the image-stabilizing lens subunit.
In accordance with a preferred aspect of the invention, in the zoom lens, the image-stabilizing lens subunit has a negative refractive power.
In accordance with a preferred aspect of the invention, in the zoom lens, the image-stabilizing lens subunit has at least one negative lens and at least one positive lens.
In accordance with a preferred aspect of the invention, in the zoom lens, the following condition is satisfied:
xe2x88x920.45 greater than (xcex12xe2x80x2xe2x88x92xcex12)
where xcex12 is a converted inclination angle of incidence of a ray entering the image-stabilizing lens subunit, and xcex12xe2x80x2 is a converted inclination angle of exit of a ray exiting from the image-stabilizing lens subunit.
In accordance with a preferred aspect of the invention, in the zoom lens, the following condition is satisfied:
10 less than (xcexdn2xe2x88x92xcexdp2)
where xcexdn2 is, when the image-stabilizing lens subunit includes only one negative lens, an Abbe number of the negative lens included in the image-stabilizing lens subunit or, when the image-stabilizing lens subunit includes a plurality of negative lenses, a mean value of Abbe numbers of all the negative lenses included in the image-stabilizing lens subunit, and xcexdp2 is, when the image-stabilizing lens subunit includes only one positive lens, an Abbe number of the positive lens included in the image-stabilizing lens subunit or, when the image-stabilizing lens subunit includes a plurality of positive lenses, a mean value of Abbe numbers of all the positive lenses included in the image-stabilizing lens subunit.
In accordance with a preferred aspect of the invention, in the zoom lens, a lens subunit disposed on the image side of the image-stabilizing lens subunit in the fourth lens unit includes a plurality of positive lenses and at least one negative lens.
In accordance with a preferred aspect of the invention, in the zoom lens, the following condition is satisfied:
10 less than (xcexdp(4R)xe2x88x92xcexdn(4R))
where xcexdp(4R) is a mean value of Abbe numbers of all the positive lenses included in the lens subunit disposed on the image side of the image-stabilizing lens subunit in the fourth lens unit, and xcexdn(4R) is, when the lens subunit disposed on the image side of the image-stabilizing lens subunit in the fourth lens unit includes only one negative lens, an Abbe number of the negative lens included in the lens subunit disposed on the image side of the image-stabilizing lens subunit in the fourth lens unit or, when the lens subunit disposed on the image side of the image-stabilizing lens subunit in the fourth lens unit includes a plurality of negative lenses, a mean value of Abbe numbers of all the negative lenses included in the lens subunit disposed on the image side of the image-stabilizing lens subunit in the fourth lens unit.
In accordance with a preferred aspect of the invention, the zoom lens further comprises an aperture stop disposed in a space close to the image-stabilizing lens subunit on the object side or the image side thereof.
In accordance with a preferred aspect of the invention, in the zoom lens, the third lens unit includes at least one positive lens and at least one negative lens.
To attain the above object, in accordance with a second aspect of the invention, there is provided a zoom lens comprising, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power arranged to move during variation of magnification, a third lens unit of negative refractive power arranged to compensate for shift of an image plane due to the variation of magnification, and a fourth lens unit of positive refractive power, wherein the fourth lens unit has an image-stabilizing lens subunit of positive refractive power including at least one positive lens and at least one negative lens and disposed within a diverging light flux exiting from the third lens unit, the image-stabilizing lens subunit being movable in such a way as to have a component perpendicular to an optical axis of the zoom lens so as to displace an image, and the following condition is satisfied:
0.45 less than (xcex1xe2x80x2xe2x88x92xcex1)
where xcex1 is a converted inclination angle of incidence of a ray entering the fourth lens unit, and xcex1xe2x80x2 is a converted inclination angle of exit of a ray exiting from the image-stabilizing lens subunit.
To attain the above object, in accordance with a third aspect of the invention, there is provided a zoom lens comprising, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power arranged to move during variation of magnification, a third lens unit of negative refractive power arranged to compensate for shift of an image plane due to the variation of magnification, and a fourth lens unit of positive refractive power, wherein the fourth lens unit has an image-stabilizing lens subunit of negative refractive power, and the image-stabilizing lens subunit is movable in such a way as to have a component perpendicular to an optical axis of the zoom lens so as to displace an image.
In accordance with a preferred aspect of the invention, in the zoom lens, the image-stabilizing lens subunit includes at least one negative lens and at least one positive lens, and the following condition is satisfied:
xe2x88x920.45 greater than (xcex12xe2x80x2xe2x88x92xcex12)
where xcex12 is a converted inclination angle of incidence of a ray entering the image-stabilizing lens subunit, and xcex12xe2x80x2 is a converted inclination angle of exit of a ray exiting from the image-stabilizing lens subunit.
To attain the above object, in accordance with a fourth aspect of the invention, there is provided a photographing apparatus comprising a zoom lens and a casing arranged to hold the zoom lens, the zoom lens comprising, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power arranged to move during variation of magnification, a third lens unit of negative refractive power arranged to compensate for shift of an image plane due to the variation of magnification, and a fourth lens unit of positive refractive power, wherein the fourth lens unit has a focal-length changeover subunit arranged to be insertable onto and detachable from an optical axis of the zoom lens and provided for changing the focal length of the zoom lens, and an image-stabilizing lens subunit disposed on the object side of the focal-length changeover subunit, and the image-stabilizing lens subunit is movable in such a way as to have a component perpendicular to the optical axis so as to displace an image.
To attain the above object, in accordance with a fifth aspect of the invention, there is provided a photographing apparatus comprising a zoom lens and a casing arranged to hold the zoom lens, the zoom lens comprising, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power arranged to move during variation of magnification, a third lens unit of negative refractive power arranged to compensate for shift of an image plane due to the variation of magnification, and a fourth lens unit of positive refractive power, wherein the fourth lens unit has an image-stabilizing lens subunit of positive refractive power including at least one positive lens and at least one negative lens and disposed within a diverging light flux exiting from the third lens unit, the image-stabilizing lens subunit being movable in such a way as to have a component perpendicular to an optical axis of the zoom lens so as to displace an image, and the following condition is satisfied:
0.45 less than (xcex1xe2x80x2xe2x88x92xcex1)
where xcex1 is a converted inclination angle of incidence of a ray entering the fourth lens unit, and xcex1xe2x80x2 is a converted inclination angle of exit of a ray exiting from the image-stabilizing lens subunit.
To attain the above object, in accordance with a sixth aspect of the invention, there is provided a photographing apparatus comprising a zoom lens and a casing arranged to hold the zoom lens, the zoom lens comprising, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power arranged to move during variation of magnification, a third lens unit of negative refractive power arranged to compensate for shift of an image plane due to the variation of magnification, and a fourth lens unit of positive refractive power, wherein the fourth lens unit has an image-stabilizing lens subunit of negative refractive power, and the image-stabilizing lens subunit is movable in such a way as to have a component perpendicular to an optical axis of the zoom lens so as to displace an image.